The rfaD gene and its gene product, ADP-L-glycero-D-mannoheptose 6- epimerase have been defined and reported by my laboratory. An efficient rfaD gene expression system and a two-step purification protocol facilitated the purification of the rfaD gene product to greater than 95% homogeneity. Physicochemical studies of the epimerase indicate that it is an NAD-containing glycosylated enzyme of 240 KD. Stereochemical, kinetic and structural studies of the epimerase are on-going. Procedures for crystallization of the epimerase have successfully yielded three crystal forms of the enzyme adequate for preliminary X-ray diffraction analysis. We have demonstrated structural and functional homologies of the rfaD gene product of Brucella abortus and the nonenteric pathogen Pseudomonas aeruginosa to its E. coli K-12 counterpart. We demonstrated the function of the rfaC gene product as heptosyl transferase I, and we have provided evidence for its significant interspecific similarity and identity. We developed a preparative polyacrylamide gel electrophoretic purification protocol for the heptosyl transferase I. Physicochemical studies of the rfaC product are on-going.